Postgres/JSON - update all array elements

Question

Given the following json:

{
  "foo": [
    {
      "bar": true
    },
    {
      "bar": true
    }
  ]
}

How can I select the following:

{
  "foo": [
    {
      "bar": false
    },
    {
      "bar": false
    }
  ]
}

?

So far I've figured out how to manipulate a single array value:

SELECT
    jsonb_set(
      '{
        "foo": [
          {
            "bar": true
          },
          {
            "bar": true
          }
        ]
    }'::jsonb, '{foo,0,bar}', to_jsonb(false)
)

But how do I set all elements within an array?

Answer 1

There is no standard function to update json array elements by key. A custom function is probably the simplest way to solve the problem:

create or replace function update_array_elements(arr jsonb, key text, value jsonb)
returns jsonb language sql as $$
    select jsonb_agg(jsonb_build_object(k, case when k <> key then v else value end))
    from jsonb_array_elements(arr) e(e), 
    lateral jsonb_each(e) p(k, v)
$$;

select update_array_elements('[{"bar":true},{"bar":true}]'::jsonb, 'bar', 'false');

      update_array_elements
----------------------------------
 [{"bar": false}, {"bar": false}]
(1 row)

Your query may look like this:

with a_data(js) as (
values(
    '{
        "foo": [
          {
            "bar": true
          },
          {
            "bar": true
          }
        ]
    }'::jsonb)
)
select
    jsonb_set(js, '{foo}', update_array_elements(js->'foo', 'bar', 'false'))
    from a_data;

                 jsonb_set                 
-------------------------------------------
 {"foo": [{"bar": false}, {"bar": false}]}
(1 row)     

Answer 2

You might want to kill two birds with one stone - update existing key in every object in the array or insert the key with a given value. jsonb_set is a perfect match here, but it requires us to pass the index of each object, so we have to iterate over the array first.

The implementation is HIGHLY inspired by klin's answer, which didn't solve my problem (which was updating and inserting) and didn't work if there were multiple keys in the object. So, the implementation is as follows:

-- the params are the same as in aforementioned `jsonb_set`
CREATE OR REPLACE FUNCTION update_array_elements(target jsonb, path text[], new_value jsonb)
  RETURNS jsonb language sql AS $$
    -- aggregate the jsonb from parts created in LATERAL
    SELECT jsonb_agg(updated_jsonb)
    -- split the target array to individual objects...
    FROM jsonb_array_elements(target) individual_object,
    -- operate on each object and apply jsonb_set to it. The results are aggregated in SELECT
    LATERAL jsonb_set(individual_object, path, new_value) updated_jsonb
  $$;

And that's it... :)

I hope it'll help someone with the same problem I had.